Bulletin of the American Physical Society
14th Annual Meeting of the Northwest Section of the APS
Volume 57, Number 7
Thursday–Saturday, October 18–20, 2012; Vancouver, British Columbia, Canada
Session C2: Nuclear Physics |
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Chair: Corina Andreoiu, Simon Fraser University Room: SFU Harbour Centre 1315 Scotiabank Lecture Room |
Friday, October 19, 2012 1:30PM - 2:06PM |
C2.00001: 25 Years of Radioactive Beams at TRIUMF Invited Speaker: John M. D'Auria It has been 25 years since the first radioactive beams were produced at TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics. These first beams, $^{37,38}$K and $^{25}$Na, were produced using the innovative TISOL (Test Isotope Separator On-Line) prototype facility and started the path to the present ISAC (Isotope Separator and ACcelerator) facility, considered one of the best accelerated radioactive beam facilities in the world today, and the new ARIEL (Advanced Rare IsotopE Laboratory) facility, presently under construction. It is time to acknowledge the role TISOL played in opening this path, and explore some of its achievements during its years of operation. TISOL enabled experiments measuring the decay of very short-lived isotopes, including information needed for energy production in novae, an atom trap to measure neutrino momenta from beta decay, a key experiment in understanding the production of carbon and oxygen in the Universe, and other studies. This presentation will give a short history of TISOL, aspects of its original technical characteristics and a summary of its scientific achievements. [Preview Abstract] |
Friday, October 19, 2012 2:06PM - 2:18PM |
C2.00002: Examining Shape Co-existence in 116Sn via the Beta Decay of 116In J. Pore, C. Andreoiu, D. Cross, R. Ashley, A. Chester, K. Starosta, G.C. Ball, P. Bender, R. Churchman, P. Voss, Z. Wang, A.B. Garnsworthy, B. Handinia, B. Jigmeddorj, P.E. Garrett, G. Demand, A.T. Laffoley, A. Liblong, R. Dunlop, C.E. Svensson, A.D. Valera, A.D. Varela, R. Kanungo, J.L. Woods, S.W. Yates The stable even-even tin nuclei have a closed proton shell at Z=50 and occupy the mid-shell region of neutrons, which has led to interest in them, and they have emerged as good candidates for shape co-existence studies. The 116Sn nucleus, which sits exactly at the mid-shell (N=66), has been extensively studied in the past through~fusion evaporation, coulomb excitation, neutron scattering and beta decay experiments, which has revealed an extensive level scheme and evidence for shape co-existence. However, with our advanced detection set-up and good beam intensity we are able to see additional weak transitions, some of which could yield evidence for another deformed excited state at 2545 keV. \newline ~ \newline The experiment was conducted at TRIUMF, Canada's National Laboratory for Nuclear and Particle Physics. A beam of 116In was used to populate states in 116Sn via beta decay. The resulting gamma rays were observed with the 8pi array consisting of 20 high-purity germanium detectors coupled with a suite of ancillary detectors. We will present the enhanced level scheme constructed from this experiment. [Preview Abstract] |
Friday, October 19, 2012 2:18PM - 2:30PM |
C2.00003: Conversion-Electron Spectroscopy of $^{116}$Sn via the $\beta $-decay of $^{116}$In David Cross, Corina Andreoiu, Jennifer Pore, G.C. Ball, V. Bildstein, A. Chester, R. Churchman, G.A. Demand, A. Diaz Varela, R. Dunlop, A.B. Garnsworthy, P.E. Garrett, B. Hadinia, G. Hackman, B. Jigmeddorj, R. Kanungo, A.T. Laffoley, A. Liblong, B. Noakes, C.E. Svensson, P. Voss, Z.-M. Wang, J.M. Wilson, J.L. Wood, S. Yates Motivated by a study of the prevalence of shape coexistence and collectivity in nuclei at closed shells [1], we have revisited the $^{116}$Sn (Z=50; N=66) nucleus, known to exhibit these characteristics [2], using a $^{116}$In beam produced via the ISOL technique at TRIUMF. The beta decay of $^{116}$In to $^{116}$Sn has been measured using the 8$\pi $ spectrometer and its suite of ancillary detectors. In this presentation we focus on the conversion-electron coincidence spectroscopy of the $^{116}$Sn nucleus, in order to augment and improve the existing knowledge of its structure via the high-statistics spectroscopic data obtained in our experiment. In particular, re-measurements of internal conversion coefficients will be discussed as they pertain to the possibility of mixing of different shapes between bands in $^{116}$Sn. [1] K. Heyde and J.L. Wood, Rev. Mod. Phys. 83, 1467 (2011). [2] S. Raman et al., Phys. Rev. C 43 521 (1991) [Preview Abstract] |
Friday, October 19, 2012 2:30PM - 2:42PM |
C2.00004: $\beta$-decay study of neutron-rich $^{102}$Rb at TRIUMF-ISAC Zhimin Wang Experimental investigations of the $\beta$-decay properties of nuclei which lie along the astrophysical r-process are becoming possible with modern facilities and detection systems. In this experiment, a $^{102}$Rb beam was produced by 500 MeV, 10 $\mu$A protons impinging on a multilayer UC$_x$ target at TRIUMF-ISAC Facility. The beam of $^{102}$Rb ions was implanted on a movable tape at the center of the 8$\pi$ spectrometer. The 20 HPGe 8$\pi$ $\gamma$-ray detectors were coupled with SCEPTAR, an hemispherical array of scintillators for $\beta$-tagging and DANTE, an array of five LaBr$_3$ detectors for fast $\gamma$-ray timing. A preliminary analysis has allowed the first identification of the $4^+$ to $2^+$ transition in the daughter nucleus, $^{102}$Sr. A near identical low-lying band structure of $^{102}$Sr with $^{98, ~100}$Sr nuclei has been observed, indicating the rigidly deformed rotational nature continues towards to the $N=66$ midshell. The current experimental measurements of $^{102}$Rb $\beta$-decay half life as well as the $\beta$-delayed neutron emission branching ratio compared with reported values, the shorter $\beta$-decay half life and the larger $\beta$-delayed neutron emission branching ratio will locally reshape astrophysical r-process predictions. [Preview Abstract] |
Friday, October 19, 2012 2:42PM - 2:54PM |
C2.00005: Optics for Nuclear Spin Polarization Scott Smale, John Behr, Spencer Behling, Alexander Gorelov, Melissa Anholm At TRINAT (TRIumf Neutral Atom Trap) the current goal is a precision measurement of the angular asymmetry of beta particles with respect to the nuclear spin, $A_{\beta}$, from the beta decay of $^{37}$K nuclei. To measure beta asymmetry to $10^{-3}$ accuracy the nuclear spins of the atoms in the trap must be spin polarized in the same direction to at least the same degree of accuracy. To achieve this level of spin polarization the degree of circular polarization of the pumping light must also be very good, with Stokes parameter S$_{3}$ better than 0.999. There are two challenges: creating well circularly polarized light and transmitting it to the cloud in the center of the experimental chamber. My talk will discuss these challenges in the context of our experiment. [Preview Abstract] |
Friday, October 19, 2012 2:54PM - 3:06PM |
C2.00006: Towards an Atomic Parity Violation Measurement with Laser Trapped Francium at ISAC R. Collister, M. Tandecki, G. Gwinner, J. Zhang, L. Orozco, J.A. Behr, M.R. Pearson, E. Gomez-Garcia, S. Aubin The neutral atom trap for parity violation measurements at TRIUMF has recently accepted its first radioactive beam. The longest lived francium isotopes have half-lives of minutes, requiring us to produce them with the online mass separator of the ISAC facility. The ion beam is embedded into a catcher made of yttrium foil where it is neutralized. Subsequently, the foil is rotated and heated to release a pulse of atomic francium into the laser trap cell. Francium isotopes 207, 209 and 221 have successfully been cooled and confined in a magneto-optical trap, a crucial first step for later experiments. The next online measurements are planned for November 2012 where two physics goals will be pursued. Firstly, the hyperfine anomaly will be probed via high precision spectroscopy on the atomic D1 transition in order to investigate the nuclear magnetization distribution. This will be followed by ionization cross-section measurements from the 7p$_{3/2}$ state to evaluate this as a potential problematic trap loss mechanism for future parity violation measurements. [Preview Abstract] |
Friday, October 19, 2012 3:06PM - 3:18PM |
C2.00007: Longitudinal Response Function of $^{3}$H from Chiral Potentials Michael Desrochers, Sonia Bacca In the electron scattering off a nucleus, the cross section is proportional to the longitudinal response function \begin{equation} R_{L}(\omega,\mathbf{q})=\sum_{f}\hspace{-13pt}\int\left|\langle\Psi_{f}|\rho(\mathbf{q})|\Psi_{0}\rangle\right|^{2}\delta\left(E_{f}-E_{0}-\omega\right), \end{equation} where $\rho(\mathbf{q})$ is the current operator. We aim at calculating it for the $^{3}$H nucleus using Chiral Effective Field Theory (EFT) potentials. Electron scattering observables are sensitive to three-nucleon forces [1], and thus, it is relevant to test EFT on reactions in the continuum. We use the Lorentz Integral Transform (LIT) to reduce the continuum problem to the solution of a bound state like equation [2] which is solved by expanding wave functions in terms of hyperspherical harmonics [3]. The response is obtained by a numerical inversion of the (LIT). Preliminary results are presented for low energies at q = 174 MeV/c, along with a comparison with experimental data and previous calculations [4].\\[0pt] [1] Bacca {\it et al.} Phys. Rev. Lett. 102, 162501 (2009)\\[0pt] [2] Efros {\it et al.} Phys. Lett. B, 338 130 (1994)\\[0pt] [3] Barnea {\it et al.} Phys. Rev. C 61, 054001 (2000)\\[0pt] [4] Efros {\it et al.} Phys. Rev. C 69, 044001 (2004) [Preview Abstract] |
Friday, October 19, 2012 3:18PM - 3:38PM |
C2.00008: BREAK |
Friday, October 19, 2012 3:38PM - 4:14PM |
C2.00009: Weak Interaction Studies with $^6 {\rm He}$ Invited Speaker: Alejandro Garcia The CENPA laboratory at the University of Washington has recently developed the world's most intense source of $^6{\rm He}$. With the aid of this new source the $^6{\rm He}$ half-life has been measured with high accuracy, solving a long standing experimental discrepancy and illuminating issues regarding the renormalization of the axial coupling constant in the nuclear medium. Recent advancements in ab-initio nuclear-structure calculations were crucial in the interpretation of the data for this light nucleus. The $^6{\rm He}$ source -delivering about $10^{10}$ atoms per second- makes possible a planned search for a signature of new physics called ``tensor currents'' to unprecedented precision. The tensor currents would be revealed either in the correlation between the direction of emission of the electron and the neutrino or in the shape of the beta spectrum in the decay of 6He. Laser trapping is being developed to be used for producing an ideal source for precise measurements. In this talk we will describe the source developments, the determination of the 6He half-life, the recent laser-trapping improvements, and the prospects for the future measurements. [Preview Abstract] |
Friday, October 19, 2012 4:14PM - 4:26PM |
C2.00010: Taming Highly Charged Radioisotopes Usman Chowdhury, Benjamin Eberhardt, Fuluni Jang, Brad Schultz, Vanessa Simon, Paul Delheij, Jens Dilling, Gerald Gwinner The precise and accurate mass of short-lived radioisotopes is a very important parameter in physics. Contribution to the improvement of nuclear models, metrological standard fixing and tests of the unitarity of the Caibbibo-Kobayashi-Maskawa (CKM) matrix are a few examples where the mass value plays a major role. TRIUMF's ion trap for atomic and nuclear physics (TITAN) is a unique facility of three online ion traps that enables the mass measurement of short-lived isotopes with high precision ($\sim 10^{-8}$). At present TITAN's electron beam ion trap (EBIT) increases the charge state to increase the precision, but there is no facility to significantly reduce the energy spread introduced by the charge breeding process. The precision of the measured mass of radioisotopes is linearly dependent on the charge state while the energy spread of the charged radioisotopes affects the precision adversely. To boost the precision level of mass measurement at TITAN without loosing too many ions, a cooler Penning trap (CPET) is being developed. CPET is designed to use either positively (proton) or negatively (electron) charged particles to reduce the energy spread via sympathetic cooling. Off-line setup of CPET is complete. Details of the working principles and updates are presented [Preview Abstract] |
Friday, October 19, 2012 4:26PM - 4:38PM |
C2.00011: Charge Breeding Techniques in an Electron Beam Ion Trap for High Precision Mass Spectrometry at TITAN T.D. Macdonald, M.C. Simon, J.C. Bale, U. Chowdhury, M. Eibach, A.T. Gallant, A. Lennarz, V.V. Simon, A. Chaudhuri, A. Grossheim, A.A. Kwiatkowski, B.E. Schultz, J. Dilling Penning trap mass spectrometry is the most accurate and precise method available for performing atomic mass measurements. TRIUMF's Ion Trap for Atomic and Nuclear science is currently the only facility to couple its Penning trap to a rare isotope facility and an electron beam ion trap (EBIT). The EBIT is a valuable tool for beam preparation: since the precision scales linearly with the charge state, it takes advantage of the precision gained by using highly charged ions. However, this precision gain is contingent on fast and efficient charge breeding. An optimization algorithm has been developed to identify the optimal conditions for running the EBIT. Taking only the mass number and half-life of the isotope of interest as inputs, the electron beam current density, charge breeding time, charge state, and electron beam energy are all specified to maximize this precision. An overview of the TITAN charge breeding program, and the results of charge breeding simulations will be presented. [Preview Abstract] |
Friday, October 19, 2012 4:38PM - 4:50PM |
C2.00012: GEANT4 simulations for in trap decay spectroscopy for electron capture branching ratio measurements using the TITAN facility Shakil Seeraji, C. Andreoiu, F. Jang, T. Ma, A. Chaudhuri, A. Grossheim, A.A. Kwiatkowski, B.E. Schultz, E. Mane, G. Gwinner, J. Dilling, A. Lennarz, D. Frekers, U. Chowdhury, V.V. Simon, T. Brunner, P. Delheij, M.C. Simon The TITAN-EC project has developed a unique technique to measure electron capture branching ratios (ECBRs) of short lived intermediate nuclide involved in double beta decay. The ECBR information is important for determination of nuclear matrix elements of double-$\beta $ decay for both double beta decay (2$\nu \beta \beta)$ and neutrino-less double beta decay (0$\nu \beta \beta )$ processes. An important feature of this technique is the use of open access penning trap. Radioactive ions are stored in the trap and their decays are observed. Electrons produced from $\beta $ decay are guided out of the trap by the Penning trap's strong magnetic field and the x-ray from EC are detected by seven Si(Li) detectors placed radially around trap using thin Be windows. This set-up provides a lower background for the x-ray detection compared to earlier ECBC measurements where the beam is implanted in mylar tape. Detailed GEANT4 simulations have been performed to characterize the efficiency of the detectors and understand their response. In addition the impact of different sizes and shapes of the ion cloud inside the trap has also been investigated to optimize the experimental set-up. [Preview Abstract] |
Friday, October 19, 2012 4:50PM - 5:02PM |
C2.00013: Precision mass measurements of highly charged ions A.A. Kwiatkowski, J.C. Bale, T. Brunner, A. Chaudhuri, U. Chowdhury, S. Ettenauer, D. Frekers, A.T. Gallant, A. Grossheim, A. Lennarz, E. Mane, T.D. Macdonald, B.E. Schultz, M.C. Simon, V.V. Simon, J. Dilling The reputation of Penning trap mass spectrometry for accuracy and precision was established with singly charged ions (SCI); however, the achievable precision and resolving power can be extended by using highly charged ions (HCI). The TITAN facility has demonstrated these enhancements for long-lived ($T_{1/2}\geq$50 ms) isobars and low-lying isomers, including $^{71}$Ge$^{21+}$, $^{74}Rb^{8+}$, $^{78}$Rb$^{8+}$, and $^{98}$Rb$^{15+}$. The Q-value of $^{71}$Ge enters into the neutrino cross section, and the use of HCI reduced the resolving power required to distinguish the isobars from 3 $\times$ 10$^5$ to 20. The precision achieved in the measurement of $^{74}$Rb$^{8+}$, a superallowed $\beta$-emitter and candidate to test the CVC hypothesis, rivaled earlier measurements with SCI in a fraction of the time. The 111.19(22) keV isomeric state in $^{78}$Rb was resolved from the ground state. Mass measurements of neutron-rich Rb and Sr isotopes near A = 100 aid in determining the r-process pathway. Advanced ion manipulation techniques and recent results will be presented. [Preview Abstract] |
Friday, October 19, 2012 5:02PM - 5:14PM |
C2.00014: Precision Mass Cartography near the Island of Inversion Aaron Gallant, Thomas Brunner, Usman Chowdhury, Stephan Ettenauer, Tegan MacDonald, Vanessa Simon, Ankur Chaudhuri, Ania Kwiatkowski, Brad Schultz, Matrin Simon, David Lunney, Jens Dilling A cornerstone of modern nuclear theory is the existence of the so-called ``magic'' numbers. Nuclei with a magic number of protons or neutrons are marked by a significant increase in binding energy. Recently much experimental and theoretical effort has been expended trying to elucidate how the magic numbers evolve towards the particle drip-lines. For example, it was recently found that new magic numbers N = 14, 16 appear far from stability, while the magic number N=20 disappears in the nuclide 32Mg. A method to investigate the evolution of the N=20 magic number is through atomic mass measurements. One of the first indications that the known magic numbers may begin to disappear was in the Na isotopic chain. It was observed that the two neutron separation energy S2n turns up at the neutron magic number N=20. This is opposite to the trend one would expect at a magic number. To investigate the disappearance of the N=20 shell closure the TITAN Penning trap mass spectrometer was employed to perform precision mass measurements in the Na, Mg and Al isotopic chains. We will present new precision mass measurements of 29-31Na, 30-34Mg and 29-34Al and discuss their role in determining the behavior of the N=20 shell gap. [Preview Abstract] |
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